Known fastening apparatus has a metal nut having a plastic cap with a detent. As protection against unintended rotation of the nut this detent engages in one of several depressions in the counterpart. During tightening, the spring-mounted detent springs from one depression to the other. The tightened nut is secured to a sufficient extent against inadvertent loosening, for example due to vibrations, by the detent engaging in a depression. However, if the nut is intended to be loosened, then this is only possible with the application of great force or with the aid of a tool with which the detent is "levered" out of the depression.
It is also known in the art to use so-called spring plates as protection against nut rotation. However, in the case of strong vibrations, such as occur frequently for example in machines in the automation sector, a spring plate is not sufficient to prevent inadvertent loosening of the fastening nut.
The object of the invention, therefore, is to improve the known fastening devices in such a way that on the one hand sufficient protection against undesired loosening of the nut is ensured and on the other hand the nut can be tightened and loosened in a simple manner.